Two 500-year floods in 15 years

The U.S. Geological Survey has preliminary data showing that this month's floods on four of Iowa's rivers--the Cedar, Iowa, Shell Rock, and Wapsipinicon--were 500-year floods. Back in 1993, many rivers in the Midwest also experienced 500-year floods, so the region has endured two 500-year floods in the past 15 years. How can this be? First of all a definition--a 500-year flood is an event that has only a 0.2% chance of occurring in a given year, based on available river flow data. Of course, reliable data only goes back a century at most, so designation of a 500-year flood event is somewhat subjective. Still, it seems rather improbable that two such huge floods should occur within such a short time span, raising the question of whether the floods were, in part, human-caused.

In a provocative story in the Washington Post today, it was pointed out that part of the flooding is due to the draining of wetlands for farming purposes. As nature's natural buffers against flooding are drained and filled to provide room for more farmland, run-off and flooding are bound to increase. Furthermore, as more levees are built to protect more valuable farmland and new developments, flood waters are pushed out of the former areas they were allowed to spread out in and forced into river channels behind the new levees. Even higher levees must then be constructed to hold back the increased volume of water they are asked to contain.

Climate change contributing to flooding?The heaviest types of rains--those likely to cause flooding--have increased in recent years (see my February blog, "The future of flooding", for more detail). According to the United Nations' Intergovernmental Panel on Climate Change (IPCC) 2007 report, "The frequency of heavy precipitation events has increased over most land areas". Indeed, global warming theory has long predicted an increase in heavy precipitation events. As the climate warms, evaporation of moisture from the oceans increases, resulting in more water vapor in the air. According to the 2007 IPCC report, water vapor in the global atmosphere has increased by about 5% over the 20th century, and 4% since 1970.

Over the U.S., where we have very good precipitation records, annual average precipitation has increased 7% over the past century (Groisman et al., 2004). The same study also found a 14% increase in heavy (top 5%) and 20% increase in very heavy (top 1%) precipitation events over the U.S. in the past century. Kunkel et al. (2003) also found an increase in heavy precipitation events over the U.S. in recent decades, but noted that heavy precipitation events were nearly as frequent at the end of the 19th century and beginning of the 20th century, though the data is not as reliable back then. Thus, climate change is likely partly to blame for increased flooding in the U.S., although we cannot rule out long-term natural variations in precipitation.

Figure 1. Forecast change in precipitation and runoff for the period 2080 to 2099 compared to 1980 to 1999. The forecasts come from the A1B scenario from multiple climate models used for the Intergovernmental Panel on Climate Change (IPCC) 2007 report.

The forecastAccording to a multi-model consensus of the climate models run for the Intergovernmental Panel on Climate Change (IPCC) 2007 report, precipitation and river runoff for the Mississippi River drainage basin are expected to increase only slightly by the end of this century (Figure 1). However, more of this rain is expected to fall in heavy precipitation events, the ones most likely to cause flooding. As a result, the U.S. needs to prepare for an increase in the number and severity of 100-year and 500-year flooding events in the coming century.

An area of low pressure is located about 750 miles south-southwest of the southern tip of Baja California. The associated showers and thunderstorm activity remains disorganized and development, if any is expected to be slow to occur.

oh crap look at this map whats hop we dont get any thing in the Caribbean or it would take it right in to New Orleans what hop this map dos not stay the same or we will be in for vary high gas and with low wind shear in the gulf

Shen - All I noted when reading the regulations is that the so-called "zero-rise" regs did not apply to agricultural land.

I see Dr. Masters cites the WaPo above as his source for blaming "part of the flooding ... due to the draining of wetlands for farming purposes". I will admit that is pretty shaky ground as a source, and I should not have taken this as authoritative and used it a springboard. Thanks for helping to put the brakes on. I will say that more research is needed to understand the problem than the word of the WaPo or even a non-Ag/non-geologist Ph.D. It is some food for further thought.

The key with 'engineering' is that we use geomorphological engineering rather than traditional civil (army corps) engineering. That is, woth WITH instead of AGAINST nature.

I agree with both of you - and with Doc M.

guygee - addendum - the pipes idea is one we used in a lawsuit settlement after my side won. Interesting thing is that it benefitted the 'loser' of the lawsuit as much or more than it did my side. It worked - that was the key.

This can be done by installing a dam with pipes through it at the downslope side of playing fields, golf courses etc. Then the area can fill during a surge and drain at a rate that can be handles downstream.

I misread your comment at first. Those are interesting ideas too. It might require that the slope be created, and that other areas drain into the man-made temporary storage site.

That is a creative solution to a problem, thanks for bringing it up, Doc!

Sorry I popped off so but you have no idea the regs that are applied to crop land and agricultural usage. Part of the joke of the engineering you are referring to surrounding housing and urban envelopment is that it assumes a number of factors that are not so. It assumes that the amount of water which will enter a stream from a given plot of land remains constant wether it is in dirt or 1/2 covered with asphalt singles and automobile amenities. It assumes that changing streams to drainage ditches has no effect in rise and fall of stream flows. It assumes that communities will actively enforce and envelopers will follow the plans and cut no corners. Additionally at least in this area the standard for a containment lagoon is that it will contain the first 15 min flush and any ensuing run off would be equivalent regardless of the rate duration etc. of any event.

I once saw a presentation from the Chesapeake Bay foundation which asserted that if one assigned a factor of 1 to the negative impact of the watershed's forested areas which have been heavily altered since the European invasion of the continent, Agriculture would receive a factor of 10, Suburbia 100 and urban areas 1000. I have been searching for the source but have not found it but it makes sense to me. It is politically much easier to focus on agricultural land and practice because you can actually make changes and other than the lobbying power of agribusiness you are talking about a minority of voters.

Sorry I popped off so but you have no idea the regs that are applied to crop land and agricultural usage. Part of the joke of the engineering you are referring to surrounding housing and urban envelopment is that it assumes a number of factors that are not so. It assumes that the amount of water which will enter a stream from a given plot of land remains constant wether it is in dirt or 1/2 covered with asphalt singles and automobile amenities. It assumes that changing streams to drainage ditches has no effect in rise and fall of stream flows. It assumes that communities will actively enforce and envelopers will follow the plans and cut no corners. Additionally at least in this area the standard for a containment lagoon is that it will contain the first 15 min flush and any ensuing run off would be equivalent regardless of the rate duration etc. of any event.

I once saw a presentation from the Chesapeake Bay foundation which asserted that if one assigned a factor of 1 to the negative impact of the watershed's forested areas which have been heavily altered since the European invasion of the continent, Agriculture would receive a factor of 10, Suburbia 100 and urban areas 1000. I have been searching for the source but have not found it but it makes sense to me. It is politically much easier to focus on agricultural land and practice because you can actually make changes and other than the lobbying power of agribusiness you are talking about a minority of voters.

It's also showing a possible system in the EATL. We'll see if it can stay consistent. As the long term upper level winds look to favorable for development in the EATL and marginally favorable for development in the Caribbean.

If you google the phrase "Knox County Tennessee Stormwater Management Manual" you can download their entire detailed stormwater engineering manual, Volumes 1 & 2, one chapter at a time. A very detailed manual.

(Of course, maintenance in another matter... A lot of localities are neglectful and just let the ponds fill with vegetation, silt and sludge, and that probably even makes things worse).

Had some pc problems over the last day or so but things are up and running.Significant rainfall down here across southeast florida this afternoon with flooding in many areas across dade/broward counties.Things should dry out this weekend otherwise nothing to worry about tropics wise. Adrian

I would note that simply creating deep ponds won't work if the ponds are then kept full. That is what has been done around here and has resulted in more flooding. Whet is needed is "freeboard" - storage space that is empty until the rain event.

This can be done by installing a dam with pipes through it at the downslope side of playing fields, golf courses etc. Then the area can fill during a surge and drain at a rate that can be handles downstream.

In effect; this mimics the wetlands that pre-existed the "improvement" (sic)

Typhoon "FRANK" has moved westward for the past six hour and is now threatening Panay and Mindoro area.

Tropical Cyclone Bulletin #10============================At 5:00 A.M. PST, Typhoon Frank located near 11.9ºN, 123.2ºE or 70 kms South of Masbate and 60 kms Northeast of Roxas City has sustained winds of 75 knots with gusts up to 90 knots.

Residents in low lying areas and near mountain slopes are advised to take all the necessary precautions against possible flashfloods and landslides. Likewise, those living in coastal areas under signal 2 and 3 are alerted against big waves or storm surges generated by this typhoon.

The public and the disaster coordinating councils concerned are advised to take appropriate action and watch for the next bulletin to be issued at 11 a.m. today.

This is true ShenValley, I used to wander around a lot in the New Hampshire hills and it was almost all very old abandoned farmland.

The heart of my point is that if you drain a swamp for farmland, you should be required to do something like dig some deep ponds to compensate for the water storage in case of flooding. According to Dr. Masters, this was not done, and according to his blog above, poor land management practices get part of the blame for the magnitude of the floods.

I am not trying to blame the small farmer, but I am thinking that big agriculture has influenced the land use regulations through the usual lobbying channels. That is what I would like to see investigated.